An investigation has been made of the two-dimensional aerodynamic characteristics of 15 NACA airfoils at four Reynolds numbers from 2.0 X 10(exp 6) to 0.7 X 10(exp 6). These data, together from previous NACA papers for the same airfoils in three Reynolds numbers from 3.0 X 10(exp 6) to 9.0 X 10(exp 6), are presented and analyzed in the present paper. The airfoils investigated consisted of 10 systematically varied NACA 6-series airfoils and 5 airfoils of the NACA 4- and 5-digit series.